This invention relates to a method and apparatus for measuring erythrocyte sedimentation rate.
The measurement of erythrocyte sedimentation or the amount of the sedimented red blood corpuscles is generally performed by pouring a blood sample consisting of a mixture of the blood and a coagulation inhibition agent into a graduated test tube, holding the tube in a vertical position for a predetermined interval, for example one or two hours, and observing the amount of the sedimented red blood corpuscles, at an interval of one hour, as shown in FIG. 1. To automatically measure the blood sedimentation rate the tube 1 filled with the blood sample is held in the vertical position, and a photoelectric detection unit 4 (see FIG. 3) including a source of light 2 on one side at the tube 1 and photoelectric transducer 3 positioned on the other side for receiving the light transmitting through the tube is moved from the upper end to the lower end of the tube 1 by means of a feed screw 6 operated by an electric motor 5 as shown in FIG. 2. With this method, the upper level of the sample before erythrocyte sedimentation is optically detected by the photoelectric detection unit 4. The unit 4 is stopped at this position and this position is memorized by a suitable memory device. After a predetermined interval the photoelectric detection unit 4 is lowered to optically detect the interface between the blood serum and the sedimented red blood corpuscles by using the difference in the light transmissibility thus determining the upper level of the sedimented red blood corpuscles. The sedimentation rate is determined by the difference between the stored level of the sample before sedimentation and the upper level of the sedimented red blood corpuscles.
The pouring of the blood sample into the narrow test tube 1 is done by a suction type injector or the like, so that an air bubble 7 would be formed in the upper portion of the tube 1 on the sample. In certain cases coagulated substance may deposite on the upper surface of the sample. For this reason, in the case of the automatic measurement, where an air bubble or the coagulated substance is present on the upper surface of the sample contained in the tube 1 the light transmittance would be reduced by the air bubble and/or the coagulated substance, so that the photoelectric detection unit 4 will be stopped at that position.
After one hour, for example, even though the blood serum 8 has been separated from the red blood corpuscles 9 due to sedimentation, the photoelectric detection unit does not move from the position of the air bubble or the coagulated substance because the photoelectric detection unit detects the light reduced by the air bubbles and/or the coagulate substance. As the result, the rate of blood sedimentation would be erroneously measured as Zero.